Thursday, May 18, 2017

Fructose and metabolic syndrome: Uric acid

which demonstrated that they (NMRs) appear to generate and use fructose as a coping stratagem for dealing with hypoxia or even anoxia. This is fascinating and leads back to research in the late 1980s, mostly looking at anoxia in liver or liver cells. I'm guessing that this liver work was funded to look at ways of improving the condition of transplant grafts. Fructose is significantly better than glucose for supporting anoxic liver cells, possibly something you might expect, possibly not. Perhaps in another post.

Anyway. So I've been looking at why fructose is different to glucose and to do this you end up asking rather difficult questions about the upper sections of both glycolysis and fructolysis.

Fructose enters the fructolytic pathway by being phosphorylated very rapidly to fructose-1-phosphate. Given a large enough supply of fructose this phosphorylation can deplete the ATP supply in a cell, most obviously in hepatocytes which bear the brunt of metabolising fructose. This takes place before aldolase generates the trioses which probably (or don't, in the case of fructose) control insulin signalling through mtG3Pdh and the glycerophosphate shuttle.

If this initial ATP depletion by fructokinase is profound it is perfectly possible to take two "waste" ADP molecules and transfer a phosphate from one to the other. This generates one ATP and one AMP. The ATP is useful to the cell and the excess AMP is degraded to uric acid.

This is all basic biochemistry.

In the Protons series I have worked on the (incorrect) basis that fructose should drive the glycerophosphate shuttle hard enough to generate RET (reverse electron transport) and so signal insulin resistance. The degree of insulin resistance should neatly reduce insulin mediated glucose supply by an appropriate amount to offset the fructose and so maintain a stable flux of ATP generation from the combined fructose and glucose. That's not quite how it appears to work. Even before the aldolase step in fructolysis, the body is starting to prepare the process of insulin resistance. This paper is not unique but shows general principles:Uric acid induces hepatic steatosis by generation of mitochondrial oxidative stress: potential role in fructose-dependent and -independent fatty liver

The title of the paper is sneaky, it doesn't give away the answer! Nor does the abstract. If you don't want to read the paper, the missing link is NOX4.

NADPH oxidase 4 (NOX4), if exposed to uric acid (present here from fructolysis induced AMP degradation), translocates to the mitochondria and starts to generate enough hydrogen peroxide* to down regulate aconitase, abort the TCA and divert citrate out of the mitochondria through the citrate/malate shuttle for DNL. This will not just affect fructose metabolism, acetyl-CoA from glucose, entering the TCA as citrate, will also be diverted to DNL.

*The NOX family appear to be the only enzymes with no function other than to produce ROS, mostly superoxide. NOX4 is unique in that it always produces hydrogen peroxide. There is uncertainty if the "E loop" of the enzyme converts superoxide to hydrogen peroxide directly or if this is a docking site for superoxide dismutase, which does the conversion as an accessory module to NOX4.

I think it is a reasonable assumption that the hydrogen peroxide generated by NOX4 will be what signals the insulin resistance induced by fructose, rather than RET via mtG3Pdh. Quite why fructose doesn't drive the glycerophosphate shuttle is a difficult question to answer. Obviously the aldolase products of fructose-1-P (fructolysis) differ from those of fructose-1-6-bisphosphate (glycolysis) but these pathways are very difficult to get at experimentally and I've not found any papers looking at what controls why dihydroxyacetone phosphate from fructolysis doesn't drive mtG3Pdh, but that appears to be the case. There are hints that some activation of the glycerophosphate shuttle does occur but NOX4 seems to be the main player. It might relate to the consumption of NADH in the conversion of glyceradehyde to glycerol and so reducing the need to decrease it using the glycerophosphate shuttle. Hard to be sure.

So. Uric acid is the evil molecular link between fructose and metabolic syndrome via NOX4. And yes, yes, you can block metabolic syndrome using allopurinol to reduce uric acid production in rats but you have to give them a sh*tload of it. After that NOX4 might be considered evil or hydrogen peroxide is evil or aconitase is evil when it's on strike. Lots of drug targets available for molecular cleansing.

My own concept is that there is the necessity to developing insulin resistance when fructose is available so as to limit glucose ingress to offset the ATP from that fructose ingress. If that is done by NOX4, so be it. The facility to deal with fructose by the generation of hydrogen peroxide is not random, it's not some accidental mistake perpetrated by evolution on hapless humans who munched on a few Crab apples or found a little honey. It is an appropriate evolutionarily response to a relatively common occurrence. The fact that uric acid mediated insulin resistance is common to alcohol metabolism as well as to fructose metabolism suggests that this mechanism is a general approach to dealing with a calorie input which takes priority over metabolising glucose.

Developing a drug along the lines of allopurinol to block uric acid production, or an inhibitor of NOX4, or a hydrogen peroxide scavenger to avoid insulin resistance is simply trying to block a perfectly adaptive response to a reasonable dose of fructose.

All that's needed to avoid a pathological response to fructose is to avoid ingesting a pathological dose of the stuff. There is actually quite a lot of evidence to suggest that physiological levels of uric acid production might be beneficial...

Thanks for the Cliff Notes version of the "Uric Acid Induces Hepatic Steatosis" article. I doubt I would have picked up on the NOX4 significance (in fact, I'm damn sure I wouldn't have), but this line struck me as being Very Bad:

Further, I notice a Richard J Johnson is the reviewing author (I think that's correct). I also notice he is an author in one capacity or another on many of 56 articles which reference the "Uric Acid" article. Seems further he wrote a couple of books on sugar. Is he possibly the same J Johnson who left comments on Hyperlipid a few years ago?

Great post which strongly supports that the sugar critics are on the right track.

Thanks for the write up, lol, I enjoyed the parts that weren't way over my head. If I may, I have struggled with gout or pseudo-gout for around 8 years. I'm obese but have lost 125 pounds via the Ketogenic diet while also incorporating intermittent fasting. This lifestyle change has made a tremendous impact on my health as I'm now off all prescriptions and rely solely on supplements and real foods. However, gout in my left big toe remains an issue. My doctor offered up allopurinol but I'd rather take care of it naturally and by addressing the root cause. I take a tart cherry capsule supplement and ingest several antioxidants a day. Interestingly the last two flare ups have come as I've started extended fasting periods. I have read other articles stating the lack of causative factors between purines and uric acid build up.

My diet is extremely low in carbs, particularly fructose and I avoid high fructose corn syrup like the plague.

altavista, I don’t really know on this one… I don’t stress about the occasional dose of either. If you had to choose then maybe fructose has a shorter time course.

Bob, I’m no lover of sugar but I suspect it causes diseases of obesity without necessarily causing obesity per se. There are papers to suggest fructose acts directly on adipocytes to increase DNL but simultaneously increases palmitate output from said adipocytes. Metabolic syndrome w/o the obesity, if the balance of effects is normal sized adipocytes. Another post there some day. PUFA seem a much better candidate as the necessary factor to make adipocytes over sensitive to normal levels of insulin so giving obesity. Not sure about Richard Johnson, might be the person.

John, dropping your uric acid levels is one way to generate an acute flare of gout. It’s a standard side effect of allopurinol. Reduced uric acid starts crystal dissolution which releases crystals in to the joint from the synovium. The other factor is palmitate. This appears to activate certain subtypes of inflammasome which can trigger a flare without reducing uric acid levels (but you can't find the glucose concentration used in cell culture, as so often). Fasting might do this but you would expect the ketones to offset the effect. Interesting. Obviously elevated FFAs in the presence of hyperglycaemia (AKA metabolic syndrome) would certainly drive a flare but that’s not the situation on keto eating. I did a little reading about citrate (Chris) and gout but can’t recall what the conclusion was! One serious problem with gout is that crystal dissolution cause flares but acute rises in uric acid don’t, they just form the crystals which have to dissolve at some stage in the future. Causing a flare.

As an aside the elevation of uric acid via AMP might be triggered by ethanol as its metabolite, acetate, reacts with ATP to give acetate-AMP and PPi and generation of acetyl-CoA releases AMP for degradation. Fatty acids have the same activation step between FFA and acyl-CoA yielding AMP and PPi. The difference is that FFA supply is controlled and both alcohol and fructose are diet intake driven.

I've been a long term lurker and an avid reader; read all your posts from start to now with great interest. I didn't recall you ever mentioning about FGF's such as 19 and 21. So did a quick search with no results. Are you aware of these and their link to measures of metabolic health? Would love to hear your thoughts.

Here is a starting point: https://academic.oup.com/mend/article-lookup/doi/10.1210/me.2015-1155

Over the years I've read snippets about FGF21 (not picked up on 19). Pattern is usually along the lines of "FGF21 is good". Quick pubmed of "FGF21" and "ketogenic diet". Ketogenic diet is just like starvation without the tedious hunger and eventual death. I kind of never got beyond that level of enquiry!!!!

Hi Peter -- thank you so much for for the analysis. Tried to grasp it! As a PS --re whether coping with anaerobic conditions is ‘abnormal’ -– since we are just glorified/evolved colonies of cooperative eukaryotes, etc, some of which have mitochondria that produce our ATP -- “Currently, the tendency is to dismiss ancestral eukaryotic anaerobic biochemistry by suggesting that all of these eukaryotes are secondarily anaerobic and that they are derived from "normal" aerobic eukaryotes. However, invoking continuous and repeated secondary events might be scientifically questionable when a more simple explanation exists: All eukaryotes may have been capable of anaerobic biochemistry from the start." https://academic.oup.com/bioscience/article/61/8/594/336975/Mitochondria-and-the-Rise-of-Eukaryotes

Trischa, this post is just a side line. There is a lot more to say but some of the core nuts and bolts are missing at the moment. It's pretty clear that fructose induces a cytoplasmic acidosis and it is this acidosis which aborts the extracellular Ca2+ influx which triggers apoptosis (or necrosis if ATP is too low for apoptosis). Whether the acidosis (cytoplasmic, not intramitochondrial) preserves a degree of proton inflow in to the mitochondria through ATP-synthase or whether it simply maintains a mitochondrial membrane potential is very hard to tease apart, either could abort apoptosis. Most of the relevant papers are from a long time ago and they didn't have the tools we have today. Today no one is asking the right questions......

"Scavenging H2O2 by antioxidant peroxidase systems in the matrix would consume electron equivalents in form of NAD(P)H [68], and thereby reduce respiration efficiency."

Another factor? From an interesting paper on peroxide function and transport. http://www.sciencedirect.com/science/article/pii/S0005273606000472

The potential for interaction between peroxisomal mitochondrial activation and activity; catalase / preoxide supply in this instance; presents food for thought.

The role of peroxisomes inaction with mitochondrial function, and their role as a source of substrate/assistance including both ACoA and catalase capacity seems to me to be greatly under-considered in the generality of mitochondrial dicussions.

They first knew that fructose goosed tryglys in humans in the 1960's from the synthetic diet work from the Apollo project - totally ignore by the medical community.

There is a correlation with Trygly and CAD - the ungrounded narrative is it feeds foam-cells, Yet, you can see that tribal peoples trygly levels are around 50 - while they consider it in the 'normal' range to be 100 in the US.

MD's that monitor people on ketogenic diets look at trygly as a way to monitor compliance.

So the question is just what does having high trygly do to peoples health over time?

Does fructose also increase FFA? I'm wondering how they keep the FFA effect on insulin resistance out of the equation?

So if someone ( perhaps the millions suffering from the global pandemic of T2D ) wanted to reverse 'insulin resistance' They might think about avoiding sugar, Linoleic acid and do a bit of weightlifting - not taking some pill..

Sugar - and carbs I think are likely truly addictive in that one of the responses to a dosage is an increase in serotonin -- which causes a downgrading of post-synaptic receptors that takes weeks to normalize. No-one ate much until the 1600's - where the sugar trade fueled slavery - as the demand kept increasing..

Side note:The B-hydroxybutyrate mentioned in the paper Petro linked to in the comments is one of those things government banned..

The history is so strange - body-builders stated taking it under the ungrounded narrative that it would increase grow-hormones.

Then there was the false narrative that it was commonly used as a date-rape drug - ignoring the fact that ethnol is the common choice.. The ban forced narcoleptics to buy dosages at 100s of times the cost of what they used before..

And now it is not possible to buy a good solvent to remove super glue.. What a world we live in - formed in no small part by false narratives. (Some people even think we can make meaningful predictions of highly complex systems by throwing computer models around..)

Significant weight loss and other situations where lots of cells are breaking down eg chemotherapy, are also associated with gout.

One common substance which slows the excretion of uric acid is aspirin. It can trigger or exacerbate gout in a catch-22 fashion ie take aspirin to relieve the pain and end up worse off. Being a part time (recreational?) gout enthusiast I learned that long ago. I have also long suspected that members of the solanacae trigger gout for me: chillies, cspsicums, eggplants tomatoes, etc.

By chance as I read this post I was also reading about salicylate intolerance.

Who'd eat fruit? It gives you both the fructose and the salicylate. Many vegetables are high in salicylate too including ... most of the solanums. Dried paprika powder is spectacularly loaded with the stuff. Curry powder too, and cinnamon.

So, if alcohol also leads to high uric acid as above by similar pathways, and fortified wine is also high in sugar and salicylates, then you have the whole classic picture of a 'rich' diet with plenty of port and sugary spicy food.

A good guide as to how to improve a gouty situation then is to eat fatty meat, not much of carefully selected fruit and veg, and stay off the booze and sugar. And the aspirin.

Pass, you have to look at it in two ways. Alcohol and fructose both raise uric acid chronically (+/-salicylate) and might predispose to urate crystal formation. But crystal dissolution is a major trigger for a flare and so are raised FFAs. Alcohol raises FFAs, fructose doesn't but see below. So how the problem starts and how it flares may be different. Although, thinking about it, I have at least one paper on the "to blog about one day" looking at fructose acting on adipocytes, which shows fructose does increase FFA release from adipocytes... If fructose causes insulin resistance what will it do in adipocytes, other than cause FFA release?

Treacherous things, plants. But I suspect I have a genetic bias to high uric acid production, perhaps a basically low elimination rate. If I take aspirin for any length of time it seems that the urate climbs high enough to start settling out. I'm not 100% convinced that it only gets inflamed when the levels go down. Monosodium urate is not very soluble? Inflammation is perhaps accessory to the removal process.

Uricase is supposed to stop it dead in its tracks, another thing to consider. Pity it's so expensive & usually only prescribed to cancer patients.

About Me

I am Petro Dobromylskyj, always known as Peter. I'm a vet, trained at the RVC, London University. I was fortunate enough to intercalate a BSc degree in physiology in to my veterinary degree. I was even more fortunate to study under Patrick Wall at UCH, who set me on course to become a veterinary anaesthetist, mostly working on acute pain control. That led to the Certificate then Diploma in Veterinary Anaesthesia and enough publications to allow me to enter the European College of Veterinary Anaesthesia and Analgesia as a de facto founding member. Anaesthesia teaches you a lot. Basic science is combined with the occasional need to act rapidly. Wrong decisions can reward you with catastrophe in seconds. Thinking is mandatory.
I stumbled on to nutrition completely by accident. Once you have been taught to think, it's hard to stop. I think about lots of things. These are some of them.

Organisation (or lack of it)!

The "labels" function on this blog has been used to function as an index and I've tended to group similar subjects together by using labels starting with identical text. If they're numbered within a similar label, start with (1). The archive is predominantly to show the posts I've put up in the last month, if people want to keep track of recent goings on. I might change it to the previous week if I ever get to time to put up enough posts in a week to justify it. That seems to be the best I can do within the limits of this blogging software!